The present invention relates to fluid distribution systems, and also to pressure equalizer-valves useful in such systems. The invention is particularly useful in water irrigation systems, and is therefore described below with respect to this application.
Water irrigation systems are commonly provided with pressure regulators and/or flow regulators to fix the outlet pressure or flow rate at predetermined values despite variations in the inlet pressure. When such regulators are used, however, it is necessary that one be provided for each branch and/or irrigation device (e.g. sprinkler, dripper) whose pressure or flow rate is to be regulated; this increases substantially the installation and maintenance costs of the system. In addition, the regulators properly preform their functions only when the inlet pressure is above a predetermined value; if the inlet pressure drops below that value, the regulator ceases to regulate. Further, since flow regulators fix the outlet flow rate at a predetermined value, a branch line having irrigating devices requiring different flow rates (e.g., high flow-rate devices for large trees, and low flow-rate devices for smaller plants) would require different value regulators for the different devices; this may not only increase the required number of regulators but usually also complicates the overall design of the system.
The present invention is not based o the conventional concept of fixing the outlet pressure or flow rate to the utilization device at a predetermined value, as in the systems using pressure regulators and flow regulators; rather, the present invention is based on the concept of substantially equalizing the inlet pressures to all the utilization devices, while permitting the inlet pressure to the utilization devices to vary with the inlet pressure applied to the input line. Thus, if the inlet line pressure increases, this will also cause an increase in the inlet pressure to all the utilization devices, but the increase in pressure will be the same for all such devices. The same occurs if the inlet line pressure is decreased. Designing the fluid distribution system according to this "pressure-equalizer" concept, which provides a number of important advantages as described more particularly below, is based on the following analysis:
The inlet pressure at each utilization device in a pressurized fluid distribution system is equal to the inlet pressure of the line, less: (1) the static pressure change resulting from the difference in elevation of the utilization device relative to that of the inlet line; and (2) the dynamic pressure change resulting from fluid flow in the line to the respective utilization device. The static pressure change may be an increase or a decrease and is a fixed value depending on the relative elevation of the respective utilization device; whereas the dynamic pressure change, which is always a decrease, arises from the flow of the fluid to the utilization device and depends on the location of the utilization device in the line. It can be shown that substantially all the dynamic pressure change occurs in the first third of the line; the dynamic pressure change in the last two-thirds of the line is so small as to be practically negligible in designing the fluid distribution system.